Then Jesus said to his disciples, “Whoever wants to be my disciple must deny themselves and take up their cross and follow me. (Matthew 16:24 NIV)
If* a Christian makes a wilful decision to surrender the authority of his life to God, a daily struggle ensues. The old self, (often referred to as the flesh in scripture) will wrestle with the Holy Spirit, who has entered in by invitation and seeks to lead the person to make choices in accordance with God's will.
Each day, each choice becomes a fork in the road, a question of "my way, or God's way?" It sounds simple, and it is. But it is not easy.
Some of the choices are so clear because they have been adopted as laws, both moral and societal, such as the choice to not take what does not belong to me, to not kill the person who bothers me, to not have a sexual relationship with someone who is not my spouse.
It is a struggle that has existed in us all since Eve was tempted to do it her way (eat, and know what God knows of good and evil) or do it God's way (and do anything she wanted EXCEPT eat from that tree). Then, as now, the choice was presented by an enemy, a manipulator who sought to deceive Eve into thinking her way was better.
I don't know if you noticed the * by the word "if" above. I said "if" because people can put their faith in Christ as their substitution on the day of judgement, but not actually follow him daily. They continue to do things their way, and wonder why the peace, joy and freedom Christ promises when you follow him, eludes them.
For me, and many others denying myself seems to be failed attempts as much as successful execution of Gods will. I struggle with self-control in my diet (gluttony), I struggle with not spending money I need to save (greed and materialism), I frequently lose patience and I do not always love others the way I should. And so many other things.
But that is where the mystery and majesty of God's grace come in to play. He knows I am not perfect, and in this life long process of transformation into the image of his Son, I never will be. He sees my heart, he sees my desire, effort and resolve to please him - not to earn salvation, but out of love and gratitude. I don't deserve his patience, his love or his mercy, but in grace, He gives me just that.
My point here is simply to explain (my thoughts on) the difference between being a Christian, who will always struggle against the flesh, and a sinner who has decided that God's way is not for them and they will not attempt to deny themselves.
Relationship with God is not developed by our good works or perfection, but through our surrender, and faith that He knows best, will give us the strength we need and we will be beside us in the battle.
This is what Jesus demonstrated when he came, he lived and he died according to God's will, not his own.
Again, the devil took him to a very high mountain and showed him all the kingdoms of the world and their splendor. “All this I will give you,” he said, “if you will bow down and worship me.” Jesus said to him, “Away from me, Satan! For it is written: ‘Worship the Lord your God, and serve him only.’ ” Then the devil left him, and angels came and attended him. (Matthew 4:8-11 NIV)
He took Peter and the two sons of Zebedee along with him, and he began to be sorrowful and troubled. Then he said to them, “My soul is overwhelmed with sorrow to the point of death. Stay here and keep watch with me.” Going a little farther, he fell with his face to the ground and prayed, “My Father, if it is possible, may this cup be taken from me. Yet not as I will, but as you will.” (Matthew 26:37-39 NIV)
God does not spare those who are perfect, who are good, who are successful. God saves those who are sold out, face down, desperately seeking his forgiveness and redemption.